Shielding effect

The shielding effect sometimes referred to as atomic shielding or electron shielding describes the attraction between an electron and the nucleus in any atom with more than one electron. The shielding effect can be defined as a reduction in the effective nuclear charge on the electron cloud, due to a difference in the attraction forces on the electrons in the atom. It is a special case of electric-field screening.

Order of shielding effect

The order of the orbitals per shielding strength is:

Reason

In hydrogen, or any other atom in group 1A of the periodic table (those with only one valence electron), the force on the electron is just as large as the electromagnetic attraction from the nucleus of the atom. However, when more electrons are involved, each electron (in the nth-shell) experiences not only the electromagnetic attraction from the positive nucleus, but also repulsion forces from other electrons in shells from 1 to n. This causes the net force on electrons in outer shells to be significantly smaller in magnitude; therefore, these electrons are not as strongly bonded to the nucleus as electrons closer to the nucleus. This phenomenon is often referred to as the orbital penetration effect. The shielding theory also contributes to the explanation of why valence-shell electrons are more easily removed from the atom.

The size of the shielding effect is difficult to calculate precisely due to effects from quantum mechanics. As an approximation, we can estimate the effective nuclear charge on each electron by the following:

Where Z is the number of protons in the nucleus and is the average number of electrons between the nucleus and the electron in question. can be found by using quantum chemistry and the Schrödinger equation, or by using Slater's empirical formulas.

In Rutherford backscattering spectroscopy the correction due to electron screening modifies the Coulomb repulsion between the incident ion and the target nucleus at large distances. It is the repulsion effect caused by the inner electron on the outer electron.

See also

References

  • L. Brown, Theodore; H. Eugene LeMay Jr; Bruce E. Bursten; Julia R. Burdge (2003). Chemistry: The Central Science (8th ed.). US: Pearson Education. ISBN 0-13-061142-5. Archived from the original on 2011-07-24.
  • Thomas, Dan (1997-10-09). "Shielding of Electrons in Atoms from H (Z=1) to Lw (Z=103)". University of Guelph. Retrieved 2018-07-12.
  • Peter Atkins & Loretta Jones, Chemical principles: the quest for insight [Variation in shielding effect]
Avocado Heights, California

Avocado Heights is an unincorporated census-designated place in Los Angeles County, California, United States. It lies in the San Gabriel Valley, near Puente Hills. On the northern border lies the unincorporated community of West Puente Valley; on the eastern border the City of Industry. A thin strip of the City of Industry runs to the south, and the Pomona Freeway and the Puente Hills are farther south. To the west is the San Gabriel River and the San Gabriel River Freeway, as well as the California Country Club. Avocado Heights is approximately 15 miles (24 km) from the downtown Los Angeles Civic Center. The population was 15,411 at the 2010 census, up from 15,148 at the 2000 census.

A significant portion of Avocado Heights remains equestrian and semi-rural, with many homes on lots of 0.5 acres 21,780 square feet (2,023 m2) or more. The proximity of polluting industries in what became the City of Industry, as well as the Puente Hills Landfill, suppressed property values throughout the post-World War II era—discouraging the development that transformed most of the San Gabriel Valley into a relatively densely developed suburban area.

Ballehage Beach

Ballehage Beach is an urban, public beach in the southern parts of Aarhus, Denmark and from 1929 it is one of the oldest sea baths in Denmark. Ballehage Beach is situated in the Marselisborg Forests on the Bay of Aarhus in the suburb of Højbjerg, south of Marselisborg Yacht Harbour and the Aarhus River mouth. Helgenæs lies across the bay to the east, a bit inland to the west is the Marselisborg Deer Park and to the north is the Varna Palace. The beach area is some 1,000 metres (1,000 yards) long and between 10 and 30 metres (30 and 100 feet) wide. It is a white sandy beach with occasional rows of boulders extending into the sea, for coastal erosion protection. Ballehage Beach is popular for sunbathing and swimming due to the shielding effect and scenic view of the nearby forest on the steep hillsides to the west. The beach has a single jetty extending some 20 metres (66 feet) into the sea, offering a platform to jump from or relax on. There are outdoor changing facilities, toilets and storage areas. The Beach is open year-round for everyone at no charge.Ballehage Beach does not have a life guard in the summer but there is a safety station with a lifesaver. It's situated in an area with heavy foot traffic, busy roads and a restaurants. Aarhus Municipality frequently tests the water for bacteria and algae and rates all beaches on a yearly basis. In 2014 and 2015 the beach has received the highest possible 3/3 rating. The water level drops off relatively rapidly and reaches a depth of 2 metres (6 feet 7 inches) some 20 metres (22 yards) from the shore. The winter bathing club Vikingebadeklubben Ballehage is based out of the facilities on BAllehage Beach.

Core charge

Core charge is the effective nuclear charge experienced by an outer shell electron. In other words, core charge is an expression of the attractive force experienced by the valence electrons to the core of an atom which takes into account the shielding effect of core electrons. Core charge can be calculated by taking the number of protons in the nucleus minus the number of core electrons, also called inner shell electrons, and is always a positive value.

Core charge is a convenient way of explaining trends in the periodic table. Since the core charge increases as you move across a row of the periodic table, the outer-shell electrons are pulled more and more strongly towards the nucleus and the atomic radius decreases. This can be used to explain a number of periodic trends such as atomic radius, first ionization energy (IE), electronegativity, and oxidizing.

Core charge can also be calculated as 'atomic number' minus 'all electrons except those in the outer shell'. For example, chlorine (element 17), with electron configuration 1s2 2s2 2p6 3s2 3p5, has 17 protons and 10 inner shell electrons (2 in the first shell, and 8 in the second) so:

Core charge = 17 − 10 = +7A core charge is the net charge of a nucleus, considering the completed shells of electrons to act as a 'shield.' As a core charge increases, the valence electrons are more strongly attracted to the nucleus, and the atomic radius decreases across the period.

Core electron

Core electrons are the electrons in an atom that are not valence electrons and therefore do not participate in bonding. The number of valence electrons of an element can be determined by the periodic table group of the element. With the exception of the transition metals in groups 3-12 and the lanthanide and actinide series, the number of valence electrons ranges from 0-8 electrons. All the non-valence electrons for an atom of that element are considered core electrons.

Core electrons are tightly bound to the nucleus. Therefore, unlike valence electrons the core electrons play a secondary role in chemical bonding and reactions by screening the positive charge of the atomic nucleus from the valence shell of electrons. In transition metals, the distinction between core and valence electrons is less distinct with electrons in the highest d-shell acting more like valence electrons than core electrons.

Effective nuclear charge

The effective nuclear charge (often symbolized as or ) is the net positive charge experienced by an electron in a polyelectronic atom. The term "effective" is used because the shielding effect of negatively charged electrons prevents higher orbital electrons from experiencing the full nuclear charge of the nucleus due to the repelling effect of inner-layer electrons. The effective nuclear charge experienced by the electron is also called the core charge. It is possible to determine the strength of the nuclear charge by the oxidation number of the atom.

Electric-field screening

In physics, screening is the damping of electric fields caused by the presence of mobile charge carriers. It is an important part of the behavior of charge-carrying fluids, such as ionized gases (classical plasmas), electrolytes, and charge carriers in electronic conductors (semiconductors, metals). In a fluid, with a given permittivity ε, composed of electrically charged constituent particles, each pair of particles (with charges q1 and q2 ) interact through the Coulomb force as

,

where the vector r is the relative position between the charges. This interaction complicates the theoretical treatment of the fluid. For example, a naive quantum mechanical calculation of the ground-state energy density yields infinity, which is unreasonable. The difficulty lies in the fact that even though the Coulomb force diminishes with distance as 1/r2, the average number of particles at each distance r is proportional to r², assuming the fluid is fairly isotropic. As a result, a charge fluctuation at any one point has non-negligible effects at large distances.

In reality, these long-range effects are suppressed by the flow of particles in response to electric fields. This flow reduces the effective interaction between particles to a short-range "screened" Coulomb interaction. This system corresponds to the simplest example of a renormalized interaction (see sections 1.2.1 and 3.2 of ).

In solid-state physics, especially for metals and semiconductors, the screening effect describes the electrostatic field and Coulomb potential of an ion inside the solid. Like the electric field of the nucleus is reduced inside an atom or ion due to the shielding effect, the electric fields of ions in conducting solids are further reduced by the cloud of conduction electrons.

Engineering physics

Engineering physics or engineering science refers to the study of the combined disciplines of physics, mathematics and engineering, particularly computer, nuclear, electrical, electronic, materials or mechanical engineering. By focusing on the scientific method as a rigorous basis, it seeks ways to apply, design, and develop new solutions in engineering.

Far side of the Moon

The far side of the Moon is the hemisphere of the Moon that always faces away from Earth. The far side's terrain is rugged with a multitude of impact craters and relatively few flat lunar maria. It has one of the largest craters in the Solar System, the South Pole–Aitken basin. Both sides of the Moon experience two weeks of sunlight followed by two weeks of night; the far side is sometimes called the "dark side of the Moon", meaning unseen rather than lacking light.About 18 percent of the far side is occasionally visible from Earth due to libration. The remaining 82 percent remained unobserved until 1959, when it was photographed by the Soviet Luna 3 space probe. The Soviet Academy of Sciences published the first atlas of the far side in 1960. The Apollo 8 astronauts were the first humans to see the far side with the naked eye when they orbited the Moon in 1968. All manned and unmanned soft landings had taken place on the near side of the Moon, until 3 January 2019 when the Chang'e 4 spacecraft made the first landing on the far side.Astronomers have suggested installing a large radio telescope on the far side, where the Moon would shield it from possible radio interference from Earth.

Gravitational shielding

The term gravitational shielding refers to a hypothetical process of shielding an object from the influence of a gravitational field. Such processes, if they existed, would have the effect of reducing the weight of an object. The shape of the shielded region would be similar to a shadow from the gravitational shield. For example, the shape of the shielded region above a disk would be conical. The height of the cone's apex above the disk would vary directly with the height of the shielding disk above the earth. Experimental evidence to date indicates that no such effect exists. Gravitational shielding is considered to be a violation of the equivalence principle and therefore inconsistent with both Newtonian theory and general relativity.The concept of gravity shielding is a common concept in science fiction literature, especially for space travel. One of the first and best known examples is the fictional gravity shielding substance "Cavorite" that appears in H. G. Wells's classic 1901 novel The First Men in the Moon. Wells was promptly criticized for using it by Jules Verne.

Juno Radiation Vault

Juno Radiation Vault is a compartment inside the Juno spacecraft that houses much of the probe's electronics and computers, and is intended to offer increased protection of radiation to the contents as the spacecraft endures the radiation environment at planet Jupiter. The Juno Radiation Vault is roughly a cube, with walls made of 1 cm thick (1/3 of an inch) titanium metal, and each side having an area of about a square meter (10 square feet). The vault weights about 200 kg (500 lbs). Inside the vault are the main command and data handling and power control boxes, along with 20 other electronic boxes. The vault should reduce the radiation exposure by about 800 times, as the spacecraft is exposed to an anticipated 20 million rads of radiation It does not stop all radiation, but significantly reduces it in order to limit damage to the spacecraft's electronics.The vault has been compared being like "armor" or like a "tank", and the electronics within, like the spacecraft's "brain". The power systems have been described as a "heart".

Without its protective shield, or radiation vault, Juno’s brain would get fried on the very first pass near Jupiter

The vault is one of many features of the mission to help counter the high radiation levels near Jupiter, including an orbit that reduces time spent in the highest radiation regions, radiation-hardened electronics, and additional shielding on components. The wires that lead out from the vault also have increased protection, they have a sheath of braided copper and stainless steel. Some other components used tantalum metal for shielding in Juno, and while lead is known for its shielding effect it was found to be too soft in this application. One reason that titanium was chosen over lead in this application was because titanium was better at handling launch stresses.The Ganymede orbiter proposal also included a design for a Juno-like radiation vault. However, because the radiation is less at Jupiter's moon Ganymede and the orbiter's path, the vault would not have to be as thick, all else being similar. One reason the radiation is strong at Jupiter, but confined to certain belts, is because it is generated by ions and electrons trapped in areas as a result of Jupiter's magnetic field. Jupiter's magnetosphere is about 20,000 times as strong as Earth's and is one of the items of study by Juno. (see also Juno's Magnetometer (MAG) instrument)

Another spacecraft with radiation shields was Skylab, which needed a radiation shield over a borosilicate glass window to stop it darkening, and several film vaults. There were five vaults for photographic film aboard the Skylab space station, and the largest weighed 1088 kg (2398 lb). Juno is the first time a spacecraft has a titanium vault for its electronics however. Radiation hardening in general is an important part of spacecraft design when it is required, and the main processor of Juno, the RAD750, has been used on other spacecraft where there are elevated radiation levels, and it is a radiation-hardened microprocessor. For example, the RAD750 was also used on the Curiosity rover, launched November 26, 2011Juno is a space probe sent to Jupiter in 2011 and it entered orbit the night of July 4, 2016. Juno is part of the New Frontiers program of NASA and was also built with some contributions by the Italian Space Agency (ASI).It was suggested by the publication Popular Science that the Europa Lander may use a radiation vault like the Juno Jupiter orbiter.

Lanthanide contraction

The lanthanide contraction is the greater-than-expected decrease in ionic radii of the elements in the lanthanide series from atomic number 57, lanthanum, to 71, lutetium, which results in smaller than otherwise expected ionic radii for the subsequent elements starting with 72, hafnium. The term was coined by the Norwegian geochemist Victor Goldschmidt in his series "Geochemische Verteilungsgesetze der Elemente".

MAVEN

Mars Atmosphere and Volatile EvolutioN (MAVEN) mission was developed by NASA to study the Martian atmosphere while orbiting Mars. Mission goals include determining how the planet's atmosphere and water, presumed to have once been substantial, were lost over time.MAVEN was launched aboard an Atlas V launch vehicle at the beginning of the first launch window on November 18, 2013. Following the first engine burn of the Centaur second stage, the vehicle coasted in low Earth orbit for 27 minutes before a second Centaur burn of five minutes to insert it into a heliocentric Mars transit orbit.

On September 22, 2014, MAVEN reached Mars and was inserted into an areocentric elliptic orbit 6,200 km (3,900 mi) by 150 km (93 mi) above the planet's surface. The principal investigator for the spacecraft is Bruce Jakosky of the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder.On November 5, 2015, NASA announced that data from MAVEN shows that the deterioration of Mars' atmosphere increases significantly during solar storms. That loss of atmosphere to space likely played a key role in Mars' gradual shift from its carbon dioxide-dominated atmosphere – which had kept Mars relatively warm and allowed the planet to support liquid surface water – to the cold, arid planet seen today. This shift took place between about 4.2 and 3.7 billion years ago.

Mediterranean climate

A Mediterranean climate or dry summer climate is characterized by rainy winters and dry summers, with less than 40 mm of precipitation for at least three summer months. While the climate receives its name from the Mediterranean Basin, these are generally located on the western coasts of continents, between roughly 30 and 43 degrees north and south of the equator, typically between oceanic climates towards the poles (where they tend to be wetter and cooler), and semi-arid and arid climates towards the equator (where they tend to be drier and hotter).

In essence, and due to the seasonal shift of the subtropical high-pressure belts with the apparent movement of the Sun, a Mediterranean climate is an intermediate type between these other climates, with winters warmer and drier (and sunnier) than oceanic climates and summers imitating sunny weather in semi-arid and arid climates.

The resulting vegetation of Mediterranean climates are the garrigue or maquis in the Mediterranean Basin, the chaparral in California, the fynbos in South Africa, the mallee in Australia, and the matorral in Chile. Areas with this climate are where the so-called "Mediterranean trinity" has traditionally developed: wheat, vine and olive.

Most large, historic cities of the Mediterranean basin, including Algiers, Athens, Beirut, İzmir, Jerusalem, Marseille, Naples, Rome, Tunis, and Valencia lie within Mediterranean climatic zones, as do major cities outside the Mediterranean basin, such as Adelaide, Cape Town, Casablanca, Dushanbe, Los Angeles, Lisbon, Perth, San Francisco, Santiago and Victoria.

Noble gas compound

Noble gas compounds are chemical compounds that include an element from the noble gases, group 18 of the periodic table. Although the noble gases are generally unreactive elements, many such compounds have been observed, particularly involving the element xenon. From the standpoint of chemistry, the noble gases may be divided into two groups: the relatively reactive krypton (ionisation energy 14.0 eV), xenon (12.1 eV), and radon (10.7 eV) on one side, and the very unreactive argon (15.8 eV), neon (21.6 eV), and helium (24.6 eV) on the other. Consistent with this classification, Kr, Xe, and Rn form compounds that can be isolated in bulk at or near standard temperature and pressure (at least in principle for the highly radioactive radon), whereas He, Ne, Ar have been observed to form true chemical bonds using spectroscopic techniques, but only when frozen into a noble gas matrix at temperatures of 40 K or lower, in supersonic jets of noble gas, or under extremely high pressures with metals.

The heavier noble gases have more electron shells than the lighter ones. Hence, the outermost electrons are subject to a shielding effect from the inner electrons that makes them more easily ionized, since they are less strongly attracted to the positively charged nucleus. This results in an ionization energy low enough to form stable compounds with the most electronegative elements, fluorine and oxygen, and even with less electronegative elements such as nitrogen and carbon under certain circumstances.

Plains of San Agustin

The Plains of San Agustin (sometimes listed as the Plains of San Augustin) is a region in the southwestern U.S. state of New Mexico in the San Agustin Basin, south of U.S. Highway 60. The area spans Catron and Socorro Counties, about 50 miles (80 km) west of the town of Socorro and about 25 miles north of Reserve. The plains extend roughly northeast-southwest, with a length of about 55 miles (88 km) and a width varying between 5–15 miles (8–24 km). The basin is bounded on the south by the Luera Mountains and Pelona Mountain (outliers of the Black Range); on the west by the Tularosa Mountains; on the north by the Mangas, Crosby, Datil, and Gallinas Mountains; and on the east by the San Mateo Mountains. The Continental Divide lies close to much of the southern and western boundaries of the plains.The Plains of San Agustin were purportedly the site of the Roswell UFO incident.

RFID skimming

RFID skimming is a method to unlawfully obtain someones payment card information.

Tractor beam

A tractor beam is a device with the ability to attract one object to another from a distance. The concept originates in fiction: the term was coined by E. E. Smith (an update of his earlier "attractor beam") in his novel Spacehounds of IPC (1931). Since the 1990s, technology and research has laboured to make it a reality, and have had some success on a microscopic level. Less commonly, a similar beam that repels is called a pressor beam or repulsor beam. Gravity impulse and gravity propulsion beams are traditionally areas of research from fringe physics that coincide with the concepts of tractor and repulsor beams.

United States gravity control propulsion research

American interest in "gravity control propulsion research" intensified during the early 1950s. Literature from that period used the terms anti-gravity, anti-gravitation, baricentric, counterbary, electrogravitics (eGrav), G-projects, gravitics, gravity control, and gravity propulsion. Their publicized goals were to develop and discover technologies and theories for the manipulation of gravity or gravity-like fields for propulsion. Although general relativity theory appeared to prohibit anti-gravity propulsion, several programs were funded to develop it through gravitation research from 1955 to 1974. The names of many contributors to general relativity and those of the golden age of general relativity have appeared among documents about the institutions that had served as the theoretical research components of those programs. The existence and 1950s emergence of the gravity control propulsion research have not been a subject of controversy for aerospace writers, critics, and conspiracy theory advocates, but their rationale, effectiveness, and longevity have been the objects of contested views.

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